This invention relates to a pyrometallurgical process for treating lead-copper-sulphur charges constituted from raw materials such as ores and concentrates, and/or from by-products such as calcines, leaching residues, fly ashes, ashes, slags, mattes, drosses and slimes, and/or from secondary metals. Such charges usually contain, besides substantial amounts of Pb, Cu and S, many desirable non-ferrous metals in minor amounts such as Ag, Bi, Ni, Co, As, Sb, Zn and Sn as well as Fe.
Heretofore such charges were usually treated by sinter-roasting followed by reduction smelting.
Sinter-roasting of sulphurized fines is generally carried out in an endless belt apparatus of the Dwight-Lloyd type. Drawbacks inherent to that process are well-known to those skilled in the art, such as the need for recycling a substantial amount of crushed sinter in order to give sufficient porosity to the sinter-bed and to avoid excessive heating thereof, the need for limiting the lead content of the bed, e.g., by addition of crushed slag, in order to avoid weakening of the bed, as well as the need for maintaining the initial sulphur content of the sinter-bed above a given value in order to avoid production of gases which are too poor in sulphur dioxide.
Reduction smelting is usually carried out in a shaft furnace. The charge consists of sinter, coke and fluxes and may also contain lumpy material and pelletized or otherwise compacted fines. The charge must contain enough sulphur to produce a copper-collecting matte phase. At least two other phases are also produced: a slag phase and a lead bullion phase. Reduction is controlled so as to extract as much of the non-ferrous metals into the matte and bullion phases as possible with minimum reduction of iron.
However, it is not possible to decrease the lead content of the slag phase below about 2% (all percentages herein are by weight) without enriching the copper-collecting matte phase with such amounts of iron that further converting treatment of the latter becomes less economical, as a result of which losses of less reducible metals such as Sn, Co and Zn are high. If the charge contains small amounts of elements such as As, Sb, Sn and Ni, which is usually the case, a fourth phase may be produced composed of an arsenical alloy which is difficult to separate from the lead bullion phase, if the matte phase contains more than about 40% Cu. Therefore, the copper content of the matte has to be limited to about 40%, so that its further converting treatment becomes less economical. Moreover, the lead content of the charge must be limited, e.g., by recycling slag, in order to avoid loss of mechanical resistance of the charge. Finally, the accumulation of numerous impurities within the lead bullion phase complicates its further refining treatment.
In view of the foregoing limitations and disadvantages of prior known treatment methods, there is need for an improved process for the pyrometallurgical treatment of lead-copper-sulphur charges.
Accordingly, it is an object of the present invention to provide a process for the pyrometallurgical treatment of lead-copper-sulphur charges, which allows collecting the lead in two different bullion phases, each of which collects selectively and separately a portion of the impurities in the charge, producing a matte whose copper content is not limited to 40%, and obtaining high extraction rates even for the less reducible non-ferrous metals present in the charge.
Another object is to provide a process for the pyrometallurgical treatment of lead-copper-sulphur charges which avoids sinter-roasting and which accepts such charges regardless of their lead contents.
These and other objects of the present invention as well as a fuller understanding thereof can be had by reference to the following description, drawings and claims.